Aerial tramways are conventionally supported from towers on which sheaves or pulleys are mounted for guided support of the wire or fiber rope on which the personnel carriers, such as chairs, gondolas, etc., are secured. As used herein, the expression "aerial tramway" shall include chairlifts, gondolas, ski lifts, trams and other wire or fiber rope mounted personnel conveying devices which are moved in an endless loop or are shuttled or reciprocated between stations. Usually the aerial tramway tower includes a pair of rocker arm assemblies to which the rope supporting sheaves are rotatably mounted. A typical rocker arm design includes a pair of sheaves mounted proximate opposite ends of a rocker arm, with the middle of the arm being pivotally mounted to a support structure. In a large rocker arm assembly there may be four rocker arms on which eight sheaves are mounted. The four rocker arms will be supported from pairs of intermediate rocker arms, and the pairs of intermediate rocker arms supported from opposite ends of a common even larger base or support rocker arm. The base or support rocker arm is, in turn, pivotally mounted to a transversely extending tower arm.
This rocker arm assembly construction allows the various rocker arms to pivot so as to accommodate and evenly support the haul rope, even when a carrier grip passes over the sheaves. The various pivotally mounted rocker arms can rock, walk or pivot to accommodate irregularities along the length of the wire rope and dynamic load changes on the rope.
One of the most important aspects of any aerial tramway rocker arm assembly is that the assembly be constructed in a manner which allows the incorporation of haul rope catching devices into the assembly. Thus, should the haul rope jump or derail from the sheaves, the rocker arm assembly should include means for catching the rope to prevent the personnel carrier from falling to the ground. Where possible, the rope catching device should redirect the rope back onto the sheaves.
Providing a rope catching structure on the inward or tower side of a rocker arm assembly is relatively easy. As used herein, the "inward" side of the rocker arm assembly shall mean the side of the assembly on which the hanger arm for the personnel carrier does not pass. When a central tower is employed having transversely extending arms on which the rocker arm assemblies are mounted, the inward side is the side closest to the central tower. The "outward" side of the rocker arm assembly is the side on which the hanger arm does pass.
Since the hanger arm does not pass over the inward side of the assembly, it is a relatively simple matter to provide a deflector arm or post which extends alongside and up above the rope proximate the lead and trailing sheaves of the rocker arm assembly. This deflector or rope catcher will prevent the haul rope from crawling up over the inside of the lead and trailing sheaves and will deflect the rope back down onto the sheave assembly.
On the outwardly facing side of the rocker arm assembly, however, the problem of catching or preventing the rope from jumping from the sheaves is much more substantial. Any rope catching structure must not interfere with passage of the hanger arm over the rocker arm assembly and the support sheaves. In prior aerial tramways, the rope catcher on the outward side of the rocker arm assembly has been provided by an arm or post which is mounted outwardly of the sheaves or rockers so as to catch the rope in the event that it should jump off of the sheaves. For most towers there will be considerable downward force on the rope as a result of the load, and the haul rope will drop downwardly immediately upon derailing from the sheaves. As it is downwardly displaced, the rope will become hooked or caught on the outside rope catcher. As will be understood, some towers will have rocker arm assemblies which hold the rope down. In those instances the rope catcher on the outside of the assemble presents little problem since the hanger arm need not pass over the outside rope catcher.
Various devices have been provided on rocker arm assemblies to shut down an aerial tramway as soon after the haul rope leaves the sheaves as possible. Typical of such prior art derailment actuated shutdown devices are the apparatus set forth in my U.S. Pat. Nos. 4,019,002 and 3,822,369 and my pending U.S. patent application Ser. No. 207,259, filed Nov. 17, 1980 now U.S. Pat. No. 4,363,945 and entitled "Cable Derailment Responsive Apparatus." One serious problem that has been encountered with prior rocker arm assemblies and rope catchers, however, has been that while the haul rope will be caught by the rope catcher upon jumping from the sheaves, the hanger arm on the next carrier will be pulled into the rope catcher before the lift can be stopped by the derailment responsive shutdown device. If the haul rope jumps the sheaves just after the hanger arm passes the sheave assembly, the aerial tramway will normally be shutdown before the next hanger arm reaches the rope catcher. Statistically, however, it is almost certain that situations will occur in which the rope will jump from the sheaves just as a hanger arm approaches the rocker arm assembly. The result will be that the hanger arm hits the rope catcher before the lift can be stopped, which can result in a violent decelleration of the rope, jumping of the haul rope over the rope catcher, or breaking of the rope catcher free of the rocker arm assembly, all with potentially dangerous consequences.
Rocker arm assemblies have typically heretofore been constructed in one of four manners. In the first case, the sheaves are cantilevered from an outward side of the rocker arms. The rocker arms in turn are cantilevered from an outward side of intermediate rocker arms, which in turn are cantilevered from the outward side of the base or assembly rocker arm. Rope catchers are provided as post or hooked shaped catchers proximate the lead and trailing sheaves and are secured to the lead and trailing rocker arms. This structure has the advantage of positioning all of the sheaves on the outward facing side of the assembly, which enables their easy replacement. A second type of prior rocker arm assembly construction is shown in my U.S. Pat. No. 4,019,002. In this patent, the sheaves are mounted in yoke-like rocker arms, which in turn are mounted in successively larger yokes, with the base or largest yoke being cantilevered from the tower arm. This structure affords certain advantages in enabling placement of rope catching posts, but it has the disadvantage of requiring pivoting of the yokes and holding of the same in a pivoted position for replacement of all but the lead and trailing sheaves.
A third prior rocker arm construction has included rocker arms in which the sheaves are supported above the various rocker arms so that the center line of the sheave axles is above the center line of the rocker arm pivot pins. This has the advantage of making the sheaves accessible for replacement, however, the mounting of rope catchers is more difficult.
In a fourth type of prior rocker arm assemblies, the sheaves are cantilevered on the outside of the rocker arm, but the rocker arm has a C-shaped cross section so that the sheaves and haul rope are suspended below the pivot points of the rocker arms. While the sheaves are self-aligning to some degree, this construction makes the outward rope catchers less able to support the haul rope due to the tendency of the sheaves to swing inwardly when loaded.
In all prior rocker arm assemblies, considerable care must be taken so that the rockers allow clearance for the hanger arm and chair parts at all possible angles of swing. The aerial tramway codes require that the rocker arm assembly be constructed so that it will allow for clearance of the hanger arm for carriers which are swung inwardly by 10 to 15 degrees.
Maintenance of prior rocker arm assemblies has been largely accomplished by means of clambering over the tramway tower arms out to the rocker arm assemblies using a platform mounted on one of the carriers and climbing onto the tower if necessary, or using a vehicle having a cherry picker, personnel carrying platform. Since many tramway towers are inaccessible to vehicles, the cherry picker approach is not suitable in many instances. Climbing over the tower arms from the ground or from a platform on a carrier, particularly when the towers are sloped and the terrain is steep, can pose a safety problem. Accordingly, in recent years aerial tramway code requirements have tended to move toward requiring a platform on the aerial tramway tower which can be used by repair and maintenance personnel to service the sheaves and the derailment shutdown apparatus of the rocker arm assemblies for the aerial tramway.
Prior rocker arm service platforms, however, have been added largely as an afterthought, and their design has not been integrated or coordinated to any significant degree with the rocker arm assemblies. Essentially, walkways or platforms have merely been mounted to the transverse tower arms, with the result that the platforms are awkward to use, unsightly, cause snow build-up, and often do not afford good access to the rocker arms. The rocker arms, moreover, were not designed, in many cases, for servicing from the inside or tower side of the rope, making tower mounted platforms of little assistance during maintenance and repair.
The rocker arm assembly mounted derailment responsive apparatus previously employed, including my above referenced inventions, have tended to employ one of two operating principles. Either a frangible element is impacted or struck by the derailing haul rope or derailment of the rope results in movement of the sheaves which is sensed and used to shutdown the tramway. There can occur, however, situations in which the haul rope does not hit the frangible element or the sheaves do not move significantly upon derailment.